High density fiber terminator/connector

ABSTRACT

A high density fiber terminator/connector and methods of making the high density fiber terminator/connector are provided. One method comprises using deep reactive ion etching to etch a plurality of holes through a silicon substrate, wherein each hole is sized to fit an optical fiber; placing an optical fiber in at least one hole; removing portions of the fibers such that one end of each fiber is substantially even with one side of the substrate; polishing a surface of the ends of the fibers and the side of the substrate that are substantially even; and forming a coating on the surface of the ends of the fibers and the side of the substrate that are substantially even.

CLAIM OF PRIORITY

The present application claims priority to U.S. Provisional ApplicationNo. 60/211,192, entitled “High Density Fiber Termination/Connector,”filed on Jun. 13, 2000, assigned to the Assignee of the presentapplication, and is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fiber optic terminators/connectors, andmore particularly to a high density fiber terminator/connector.

2. Description of the Related Art

Common fiber optic terminations/connectors terminate one fiber at atime. There are several connector styles (e.g., FC/PC, LC), but in allcases, a single fiber is inserted and glued in a precision ferrule,which is typically made of ceramic. The end of the ferrule and fiber arepolished together to provide a smooth surface or a desired shape.

When multiple fibers are connected together, each fiber is terminatedwith an FC/PC connector as described, and the fibers are connectedtogether one pair at a time. This process is extremely time-consumingand costly when connecting a large number of fibers together.

State of the art high density fiber connectors use micromachinedv-grooves in which the fibers are located in v-shaped channels. Thistechnology results in linear arrays of fibers, where the relativepositioning of the fibers is limited by the fabrication precision (orimprecision) of the fiber v-grooves and by a diameter uniformity (ornon-uniformity) of the fibers. When v-grooves are stacked to providetwo-dimensional arrays of fibers, the relative position accuracy isfurther reduced and results in increased insertion loss in theconnection of two such arrays.

SUMMARY OF THE INVENTION

A high density fiber terminator/connector and methods of making the highdensity fiber terminator/connector are provided in accordance with thepresent invention. One method uses silicon micro-machining to terminatemultiple fibers simultaneously. This simplifies the process and improvesthe alignment of connecting multiple fibers together or positioningmultiple fibers together to free-space optical elements.

One method uses Deep Reactive Ion Etching (DRIE) to make precise holesin a silicon wafer. The holes in the silicon may be arranged in anydesired pattern by using, for example, a mask fabrication process withelectron-beam writing of the mask, such as photolithography masking. Asingle photolithographic mask provides extremely high precision locationpositioning, and the relative position of each fiber in the holes can beaccurately controlled. The accuracy in the relative positioning of thefibers ensures that all fibers are simultaneously aligned. Thus,photolithographic masking and deep reactive ion etching enable thefabrication of connectors for a plurality of fibers. Photolithographicmasking and deep reactive ion etching also allow multiple fibers to beaccurately aligned to free-space optical components.

One aspect of the invention relates to a method of making an opticalfiber terminator. The method comprises using deep reactive ion etchingto etch a plurality of holes in a silicon substrate, wherein each holeis sized to fit an optical fiber; and placing an optical fiber in atleast one hole.

Another aspect of the invention relates to an optical fiber terminatorin an optical switch. The optical fiber terminator comprises a siliconsubstrate with a plurality of holes formed by deep reactive ion etching,wherein each hole is sized to fit an optical fiber.

Another aspect of the invention relates to an optical fiber terminatorwith holes formed to allow insertion of fibers at an angle with respectto the substrate surface.

Another aspect of the invention relates to a method of making an opticalfiber terminator. The method comprises etching a plurality of holes in asilicon substrate, wherein each hole is sized to fit an optical fiber;forming a plurality of flaps in the substrate around each hole, theflaps being configured for kinematic alignment of an optical fiber ineach hole; and placing an optical fiber in at least one hole.

Another aspect of the invention relates to an optical fiber terminator,which comprises a silicon substrate. The silicon substrate comprises aplurality of holes etched in the silicon substrate, wherein each hole issized to fit an optical fiber. The silicon substrate also comprises aplurality of flaps formed in the substrate around each hole. The flapsare configured for kinematic alignment of an optical fiber in each hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one embodiment of an array of holes etched into asilicon wafer/substrate.

FIG. 2 illustrates one embodiment of a plurality of optical fibersinserted in a plurality of holes of a portion of the substrate of FIG.1.

FIG. 3 illustrates one embodiment of angling a plurality of holes in asubstrate to allow fibers to be positioned and pointed at a specificangle.

FIGS. 4A-4B illustrate one embodiment of a substrate with a plurality ofholes and a plurality of vertical flaps positioned at an equal distancefrom each other around each hole.

FIG. 5 illustrates the wafer of FIG. 2 with top ends of the fibersremoved.

FIG. 6 illustrates one embodiment of a plurality of substrate componentsremoved from a base substrate.

FIG. 7 illustrates one embodiment of a coating formed on one side of thesubstrate and fibers in FIG. 5.

FIG. 8 illustrates one embodiment of the substrate in FIG. 5 with aplurality of MEMS components inserted in etched recesses.

FIG. 9 illustrates one embodiment of the substrate in FIG. 5 withalignment notches, which are used to align the fiber array to a lensarray.

FIG. 10 illustrates one embodiment of two aligned fiber arrays.

FIG. 11 illustrates another embodiment of two aligned fiber arrays.

FIG. 12 illustrates one embodiment of an angled fiber array.

FIG. 13 illustrates a top view of another embodiment of kinematicalignment features between two fiber arrays.

FIG. 14 illustrates one embodiment of a substrate with a plurality ofetched holes and a plurality of recesses formed on one surface of thesubstrate.

DETAILED DESCRIPTION

FIG. 1 illustrates one embodiment of an array of holes 102 (referred toherein individually or collectively as ‘102’) etched into a siliconwafer/substrate 100. The substrate 100 may be between about 200 micronsto about 650 microns in thickness. In one embodiment, the substrate 100is 600 microns thick.

In one embodiment, the holes 102 are etched with Deep Reactive IonEtching (DRIE) processes. The holes in the silicon substrate 100 may bearranged in any desired pattern by using, for example, a maskfabrication process with electron-beam writing of the mask, such asphotolithography masking. A mask is a layer with openings in desiredlocations to expose an underlying material for etching. A singlephotolithographic mask provides extremely high precision locationpositioning. Masks written by electron-beam lithography typically haveabout 10 nm to 100 nm accuracy in positioning the locations of featuresin the mask. Thus, the relative position of each fiber in the holes canbe accurately controlled.

The substrate 100 may have any number of holes 102 etched in any desiredpattern. Each hole 102 is sufficiently sized to allow an optical fiber200 (FIG. 2) to fit through the hole 102 (FIG. 1). In one embodiment,each hole is formed to closely match the diameter of an optical fiber,which is typically 125 microns.

FIG. 2 illustrates one embodiment of a plurality of optical fibers200A-200C (referred to herein individually or collectively as ‘fiber200’) inserted in a plurality of holes 102A-102C of a portion of thesubstrate 100 of FIG. 1. In FIGS. 2-5 and 7-12, a small number of fibersand holes are shown, but the methods described herein may be applied toa very large number of fibers and holes.

A fiber (core plus cladding) 200 is typically about 125 microns indiameter. The core of a fiber 200 is typically about 9 microns indiameter, but the core is conventionally not easily separable from thecladding of the fiber 200 because both the core and the cladding aretypically made out of glass. The coating or buffer 204 around the fiber200 typically comprises plastic and may be separated from the fiber 200.The diameter of the buffer 204 is typically between 250 microns and 900microns.

In one embodiment, each hole 102 in FIG. 2 provides a 5-micron spacebetween an exterior surface (e.g., cylindrical) of a fiber 200 and thehole 102. Thus, one embodiment of the hole 102 is about 135 microns indiameter to provides a 5-micron space between an exterior surface (e.g.,cylindrical) of a fiber 200 with a 25 micron diameter and the hole 102.Alternatively, if a fiber 200 is 125 microns in diameter, and each hole102 is 130 microns in diameter, there is a 2.5-micron clearance on eachside for the fiber 200 to pass through the hole 102. In anotherembodiment, if a fiber 200 is 125 microns in diameter, and each hole 102is 127 microns in diameter, there is a 1-micron clearance on each sidefor the fiber 200 to pass through the hole 102. In one embodiment, atleast 2 holes are about 10 to about 140 micros in diameter.

In one embodiment, each hole 102 is substantially cylindrical in shape.In other embodiments, each hole 102 may be non-cylindrical, such as atriangle, a rectangle or a pentagon.

The optical fibers 200A-200C in FIG. 2 are stripped (removing theirbuffer coating 204A-204C and exposing the bare fiber 200A-200C), a smallamount of glue 206A-206C is applied to the fiber coatings 204A-204C, andthe bare fibers 200A-200C are slipped into the holes 102A-102C in thesilicon wafer 100. There are many types of glue that can be used, suchas a thermal cure epoxy, which cures at 120 degrees Celsius from Epotek.

FIG. 3 illustrates one embodiment of angling a plurality of holes304A-304B in a substrate 300 to allow fibers 302A-302B to be positionedand pointed at a specific angle. The holes 304A-304B in FIG. 3 may beformed with any suitable process, such as deep reactive ion etching.Each hole 304 may also contain micro-machined kinematic alignmentmechanisms to position the optical fiber at the center of the hole 304.Micromachined kinematic alignment mechanisms are described herein and inthe U.S. Provisional Application referenced above and incorporated byreference.

FIG. 12 illustrates one embodiment of an angled optical fiberarray/terminator 1200. In FIG. 12, deep reactive ion etching forms aplurality of holes 1204A-1204C in the substrate. A front surface 1208 ofthe substrate may have a hole 1204 sized to fit an optical fiber 1202and a locator 1206 at the edge of the slotted hole 1204 to position afiber 1202 precisely on that surface 1208. In other words, each hole1204 is sized to fit an optical fiber 1202 in one direction 1210A butoversized in another direction 1210B. Thus, each slotted hole 1204allows a fiber 1202 to be inserted at an angle with respect to thesubstrate surface 1208.

The angled insertion of the fiber arrays 300, 1200 in FIGS. 3 and 12provides low back-reflection, which is important when the fiber array300 or 1200 is used as a termination into free-space (an unguided mediumwith a different optical index of refraction). Back-reflection may befurther reduced by coating the fiber array 300 or 1200 with ananti-reflection coating. Terminating fibers 304A-304B and 1202A-1202C atan angle also allows a ball lens to collimate light, such that thecollimated light comes out at an angle with respect to the substratewith low aberrations. If a graded index lens or aspheric lens is used,then it is important to tilt the lens with respect to the fiber array300 or 1200 in order to provide collimated light with low aberrations.

In another embodiment, there are no locators 1206 near the front side,and loading (e.g., with other substrates or devices) is used toprecisely position the fibers 1202A-1202C at an angle.

FIGS. 4A-4B illustrate one embodiment of a substrate 400 with aplurality of holes 408A-408B and a plurality of vertical flaps 404A-404Fpositioned at an equal distance from each other around each hole 408.FIG. 4B is a top view. Although three flaps 404A-404C, 404D-404F areshown for each hole 408A, 408B, there may be less than three or greaterthan three flaps for each hole 408A, 408B, in other embodiments. Theflaps 404A-404F may be formed by deep reactive ion etching portions ofthe silicon wafer 400. The first set of flaps 404A-404C support a firstfiber 402A equally and center the fiber 402A within the first hole 408A.Similarly, the second set of flaps 404D-404F support a second fiber 402Bequally and center the fiber 402B within the second hole 408B. The flapsprovide kinematic alignment or self-centering of a fiber 402 in a hole408, which overcomes the problem of etching non-uniformities in thewafer 400.

In FIG. 4A, each hole 408 may be tapered to allow a fiber 402 to moreeasily slide into the hole 408. In another embodiment, each hole 408 inFIGS. 4A-4B is not tapered.

FIG. 5 illustrates the wafer 202 of FIG. 2 with top ends of the fibers200A-200C removed, e.g., by cleaving or etching. The structure 500 inFIG. 5 may be referred to as a ‘fiber array,’ a ‘fiber connector’ or a‘fiber terminator.’ In one embodiment, a top side 502 of the entiresilicon wafer 202 in FIG. 5 and the glued fibers 200A-200C is polishedby a lapping and polishing process. The lapping and polishing processmay include the use of chemical mechanical polishing (CMP) slurries, orusing polishing pads with Alumina grit of various sizes that arelubricated with water. Some polishing processes are known in the art,and some recipes are provided by vendors of polishing equipment.

One of the advantages of the structure 500 in FIG. 5 is that all fibers200A-200C may be polished simultaneously. Once the ends of the fibers200A-200C are polished, the wafer 202 in FIG. 5 may be separated intoindividual components, as shown in FIG. 6.

FIG. 6 illustrates one embodiment of a plurality of substrate components602A-602D removed from a base substrate 604 (as shown by the arrow). Theseparation may be done by various methods, including but not limited todicing with a diamond saw.

FIG. 7 illustrates one embodiment of a coating 702 formed on the topside 502 of the substrate 202 and fibers 200A-200C in FIG. 5. In oneembodiment, before separating the components 602A-602D (FIG. 6) andafter polishing, an anti-reflection (AR) coating 702 is applied bydepositing films of various materials on the top side 502 the siliconwafer 202 where the fiber ends have been polished. In one embodiment,the AR coating 702 uses multiple layers of dielectric materials, wherethe materials and designs may vary. Multiple layer dielectrics forminterferometric effects, which are used to eliminate reflection from thesurface 502 and provide almost 100% transmission.

In other embodiments, the coating 702 may comprise a chemicallysensitive film for chemical sensors, or a metal coating for totalreflection. The coating 702 is a way to make a sensor or to improve theoptical characteristics of the fiber/ambient interface 502.

The processed substrates described above may be combined withmicroelectronic mechanical system (MEMS) components, such as smallmicro-machined movable mirrors and electronics. The MEMS components maybe placed in recesses in the silicon wafer 202, as shown in FIG. 8, toprevent the MEMS components from being damaged during a polishingprocess.

FIG. 8 illustrates one embodiment of the substrate 202 in FIG. 5 with aplurality of MEMS components 804A, 804B inserted in etched recesses802A, 802B. One advantage of the structure 800 in FIG. 8 is that theoptical fibers 200A-200C are aligned to the MEMS components 804A, 804Busing photolithography masking, which provides very good alignment. Asingle photolithographic mask may be used when the MEMS recesses 802A,802B and the fiber holes in FIG. 8 are etched during the same etchingprocess, such as deep reactive ion etching. A single photolithographicmask provides extremely high precision location positioning between allcomponents. Masks written by electron-beam lithography typically haveabout 10 nanometer—100 nm accuracy in positioning the locations offeatures in the mask. The structure 800 in FIG. 8 may be used infabricating a high density, MEMS fiber optic switch.

FIG. 9 illustrates one embodiment of the substrate 202 in FIG. 5 withalignment notches 908A, 908B, which are used to align the fiber array900 to a lens array 902. In one embodiment, the alignment notches 908A,908B and the fiber holes in FIG. 9 are etched into the silicon wafer 202during the same etching process, such as deep reactive ion etching. Thealignment notches 908A, 908B are aligned with respect to the fiber holesin the substrate 202 with lithographic precision.

The lens array 902 in FIG. 9 comprises a plurality of lenses 904A-904Cprotruding stubs 906A, 906B, which are intended to fit into the notches908A, 908B. In another embodiment, notches are etched into the lensarray 902 and stubs are formed (e.g., by etching the surface of thesubstrate 202) in the fiber array 900. In other embodiments, instead ofa lens array 902 with lenses 904A-904C as shown in FIG. 9, the lensarray 902 may comprise diffraction gratings, MEMS components, oranything that a user desires to align with the fiber array 900.

The fiber terminators described herein may be used for connectingfibers, such as standard single fiber connectors. In addition, thephotolithographic alignment techniques described herein may beadvantageously used to align two fiber arrays. In one embodiment,alignment features are formed to register precisely between the twofiber connectors. For example, one connector may have a protrudingfeature, while another connector may have a recess feature. On eachfiber connector, the alignment features are aligned with the fiber holeswith lithographic precision. When the features of two connectors mate,the fibers of one connector are aligned with the fibers of the otherconnector with an accuracy of about one micron or better. Tightalignment tolerances are desired in order to have a low insertion lossin the connector.

In one embodiment, one fiber in one fiber array physically contacts acorresponding fiber in another array, such that there is no air gapbetween the fibers. An air gap produces a variable loss due to theresulting interferometric effects. Two possible implementations ofaligned fiber arrays are shown in FIGS. 10 and 11.

FIG. 10 illustrates one embodiment of two aligned fiber arrays 1000,1010. In FIG. 10, the fiber arrays 1000, 1010 are aligned by visuallyaligning holes 1002A, 1002B in the two wafers 1000, 1010 or using one ormore pins 1004A, 1004B that would slide through the holes 1002A, 1002B.

FIG. 11 illustrates another embodiment of two aligned fiber arrays 1100,1102. Wafer pieces 1104A, 1104B are patterned to fit in alignment grovesetched into the two fiber wafers 1100, 1102.

FIG. 13 illustrates a top view of another embodiment of kinematicalignment features between two fiber arrays or wafers. In FIG. 13, threealignment slots or grooves 1300A-1300C are properly designed and etchedinto one silicon wafer. On another silicon wafer, three small knobs1302A-1302C are formed that align into the three grooves 1300A-1300C,which have substantially the same width as the knobs 1302A-1302C but arelonger.

In one embodiment, a plurality of holes are formed in a substrate 400 asin FIGS. 4A and 4B with a process other than deep reactive ion etching,and kinematic alignment flaps 404A-404F are formed in the substrate 400with a process, such as deep reactive ion etching.

FIG. 14 illustrates one embodiment of a fiber termination 1408 with aplurality of etched holes 1410 and a plurality of recesses 1404 formedon one side 1406 of the substrate 1400. The holes 1410 are etched withone or more processes as described above. The recesses 1404 are formedby removing material from selected parts of the ‘front’ side 1406 of thesubstrate 1400. The recesses 1404 may be formed by wet etching, plasmaetching, laser ablation, sand blasting or some other suitable method. Inone embodiment, substrate material is removed everywhere on the frontside 1406 of the substrate 1400 except a ring of substrate materialaround each hole 1410. In one embodiment, the recesses 1404 are formedbefore a plurality of fibers 1402 are inserted in the holes 1410.

In one embodiment, after the fibers 1402 are inserted in the holes 1410,the front side 1406 of the substrate 1400 and the fiber ends arepolished. With the recesses 1404 on the front side 1406, a relativelysmall amount of substrate material (e.g., the rings) located around thefibers 1402 is polished with the fiber ends. Thus, the substrate 1400with recesses 1404 allows more uniform polishing of the ends of thefibers 1402 and less wear of the polishing surface.

In addition, the substrate 1400 with recesses 1404 facilitates thephysical connection of two fiber connectors, as shown in FIGS. 10 and11. When pressure is applied between the two connectors, the pressure islocated near the fiber ends to provide low insertion loss.

The above-described embodiments of the present invention are merelymeant to be illustrative and not limiting. Various changes andmodifications may be made without departing from the invention in itsbroader aspects. The appended claims encompass such changes andmodifications within the spirit and scope of the invention.

What is claimed is:
 1. A method of making an optical fiber terminator,the method comprising: using deep reactive ion etching to etch aplurality of holes through a silicon substrate, wherein each hole issized to fit an optical fiber; placing an optical fiber in at least onehole; removing portions of the fibers such that one end of each fiber issubstantially even with one side of the substrate; polishing a surfaceof the ends of the fibers and the side of the substrate that aresubstantially even; and forming a coating on the surface of the ends ofthe fibers and the side of the substrate that are substantially even. 2.The method of claim 1, further comprising using photolithography maskingbefore the etching to position the holes.
 3. The method of claim 1,wherein at least one hole is formed to allow angled insertion of afiber.
 4. The method of claim 1, wherein the substrate is more than 200microns thick.
 5. The method of claim 1, wherein at least two holes areabout 10 to about 140 microns in diameter.
 6. The method of claim 1,wherein the coating comprises an anti-reflective coating on the surfaceof the ends of the fibers and the side of the substrate that aresubstantially even.
 7. The method of claim 1, wherein the coatingcomprises a chemically sensitive film coating on the surface of the endsof the fibers and the side of the substrate that are substantially even.8. The method of claim 1, wherein the coating comprises a metal coatingfor reflection on the surface of the ends of the fibers and the side ofthe substrate that are substantially even.
 9. The method of claim 1,further comprising gluing an optical fiber in a hole in the substrate.10. An optical fiber terminator comprising: a silicon substrate with aplurality of through holes formed by deep reactive ion etching, whereineach hole is sized to fit an optical fiber; at least one optical fiberinserted in a through hole, an end of the optical fiber beingsubstantially even with a side of the silicon substrate; and an opticalcoating deposited over the end of the fiber and the side of thesubstrate that are substantially even.
 11. The terminator of claim 10,wherein at least one hole is formed to allow angled insertion of afiber.